Release sheets are widely used in a variety of commercial applications. For example, in food packaging, it is desirable that the food articles not stick to the paper of the carton or other wrappings. Articles such as decals, labels, tapes, etc., which employ a pressure-sensitive adhesive utilize a protective release sheet over the adhesive. When such a product is used, the release sheet is peeled off and discarded and the exposed pressure-sensitive tape pressed onto the surface where the decal, label, or tape is to be placed. A common variety of release paper is one wherein one side of the paper (the release side) is coated with a polymeric siloxane material. It is also known to coat substrates such as paper with a thermoplastic material such as polyethylene and then overcoat the thermoplastic layer with an overcoating of a polymeric siloxane material.
Although these types of release sheets have been widely used, there continues to be a need to improve the properties thereof, particularly, when the release sheet is based upon the use of a paper substrate. It is desirable to develop procedures and composites which exhibit improved bonding between the siloxane layer and the underlying substrate and to reduce the tendency of silicone release materials to adhere or transfer to other surfaces. Another significant problem exhibited by some composites such as composites using a polymeric film as the base substrate, particularly when exposed to severe humidity and temperature conditions is curling due to the dimensional instability of the composite. For example, if composites curl as they are passed through a printer such as a laser printer where the composite is exposed to high temperatures, the composite may jam in the printer and/or the desired printed image will be fuzzy or uneven and unacceptable. The tear strengths of composites, particularly when used as decals, labels and tape also are important. It is desirable that the decals, labels and tape be easily removed without tearing, particularly if they are to be reused. A particularly desirable property of composites, particularly composites to be used as decals and labels is their ability to retain their flat configuration under extreme conditions such as high or low humidity, high or low temperature, etc., over a period of time. Decals and labels have a tendency to be dimensionally unstable and cuff when subjected to such conditions.
U.S. Pat. No. 3,749,593 describes a laminate material which is produced by coating a substrate with a first silicone release agent coating containing a curing catalyst, a curing accelerator and/or an adhesion promoter and subsequently overcoating said first silicone release coating with a second silicone release agent coating containing a curing agent but no cure accelerator or adhesion promoter. The laminates are particularly useful as release sheets. The substrate may be a paper substrate having bonded to one surface thereof, or to both surfaces, a polyolefinic material.